The high information rate acquisition method wherein downhole pickups are connected to the surface by means of an electric conductor is well-known. This method is conventionally implemented by setting, in the inner space of the drill string, a wireline type cable and generally by using a side-entry sub allowing the cable to run through the annular space, thus enabling drillpipe adding operations in order to follow the deepening of the borehole. The presence of the cable is very disadvantageous insofar as the rotary type drilling technique has to be abandoned and replaced by drilling with a downhole motor.
The use of special drillpipes known as "wired" pipes is also well-known, i.e. each pipe comprises an electric link and two end connectors for connecting electrically the pipes as well as the tool joints. The drill string entirely made up of these special pipes is very costly and, furthermore, the multiplicity of contacts (as many contacts as pipes about 10 meters long) is likely to decrease the insulation of the electric line, which might limit the information transmission capacity in case of deep drilling.
Transmissions by pressure waves in the drilling mud or by electromagnetic waves are also well-known. With these techniques, the information rate remains low, in any case incompatible with the continuous transmission of vibrational phenomena, for example the shakes due to a downhole seismic source or the shakes emitted by an impulsive type surface source in order to perform a VSP or Vertical Seismic Profiling.